Introduction to Web Services - · PDF file Java API for XML Web Services (JAX-WS) ! RESTful Web Services ! Java API for RESTful Web Services (JAX-RS) 2. Introduction to Service-Oriented

Introduction to Web Services

Held as part of the lecture series on

Web Engineering at Vienna University of Technology

May 2014

Business Informatics Group Institute of Software Technology and Interactive Systems 
 Vienna University of Technology Favoritenstraße 9-11/188-3, 1040 Vienna, Austria
 phone: +43 (1) 58801-18804 (secretary), fax: +43 (1) 58801-18896
 [email protected], www.big.tuwien.ac.at

Web Engineering Web Services

Philipp Liegl

Outline of today’s talk

▪ Introduction to Service-Oriented Computing !

▪ SOAP !

▪ WSDL !

▪ UDDI !

▪ Java API for XML Web Services (JAX-WS) !

▪ RESTful Web Services !

▪ Java API for RESTful Web Services (JAX-RS)

2

Introduction to Service-Oriented Computing

3

Context of Web Services: Distributed Information Systems

▪ Layers of an information system ▪ Presentation layer

▪ Communication interface to external entities ▪ Graphical user interface for human users 


or non graphical user interface for 
 other programs

▪ Application logic layer ▪ Implements operations requested by clients


through the presentation layer ▪ Resource management layer

▪ Deals with different data sources of an
 information system

▪ Distributed systems are split up into parts ▪ Run simultaneously on multiple computers ▪ Communicate over a network

presentation layer

application logic layer

resource management layer

client

TU W

IE N

W E

In fo

rm at

io n

S ys

te m

Machine to machine communication Getting applications to talk to each other

presentation layer

application logic layer

resource management layer

client

TU W

IE N

W E

In fo

rm at

io n

S ys

te m

application logic layer

resource management layerA

n ot

h er

in fo

rm at

io n

s ys

te m

client

presentation layer

application logic layer

4

Introduction to Service Oriented Computing

5

Tag Cloud

What is a service?

Introduction to Service-Oriented Computing

6

Heterogeneity as the main obstacle for seamless communication of distributed information systems

Windows Server 2008 UNIX System

Flight information and booking application

(programmed in C)

Travel information and booking application

(programmed in Java)

Travel agency "The agency" Airline "The airline"

seamless interaction?

• Mismatch in operating system, language, platform, etc. • Service-oriented computing is an emergent paradigm that helps to overcome

these mismatches

• Example: Yield management in the airline industry requires close system interaction in order to retrieve the most current prices

Introduction to Service-Oriented Computing

7

Application integration using services

Windows Server 2008 UNIX System

Flight booking application (programmed in C)

Flight information application

(programmed in Java)

Travel agency "The agency" Airline "The airline"

• Service vs. Web Service • Services are business functions which an enterprise offers to its business

partners • A possible implementation of Services are Web Services • However, other concepts may also be used to implement a Service, e.g.,

ebXML

Se rv

ic e

Se rv

ic eRequest

Response

Introduction to Service-Oriented Computing

8

Important terms in service-oriented computing

• (Web) Services are self-contained modules that can be described, published, located, orchestrated, and programmed using XML-based technologies over a network !

• Service providers are organizations that provide the service implementations, supply their service descriptions, and provide related technical and business support !

• Service clients are end-users and organizations that use some service !

• Service aggregators are organizations that consolidate multiple services into a new, single orchestrated service offering that is commonly known as business process. !

• A service-oriented architecture (SOA) is a logical way of designing a software system to provide services to either end-user applications or to other services distributed in a network, via published and discoverable interfaces.

Introduction to Service-Oriented Computing

9

Characteristics of Web Services (WS)

• WS semantically encapsulate discrete functionality • A Web Service is a self contained software module that performs a single task (e.g.

weather forecast by passing the zip-code as parameter) • WS share a contract

• In order to allow interaction of services, a formal contract must be established, that defines the exact terms of an information exchange between a service client and a service provider

• WS abstract underlying program logic • A service exposes a certain functionality to a client. How that functionality is achieved

(e.g., which program language is used, or which database is used) remains invisible to the caller

• WS are loosely coupled software modules • A service interface is defined in a neutral manner, independent of the underlying

platform, operating system, or programming language • Due to their neutral interfaces, services are not hard-wired. Thus, a service may be easily

exchanged by another service, without much implementation effort • WS are reusable

• A service may be reused by multiple applications

Introduction to Service-Oriented Computing

10

Characteristics of Web Services II (WS)

• WS can be dynamically found and included in applications • A WS provides programmable access. Thus, a WS may be embedded in a

remotely located application, i.e., a service may be composed. • Unlike Web Sites, Web Services are not targeted at human users • They are called by and exchange data with other software modules and

applications. • WS are described in terms of a standard description language

• Web Service Description Language (WSDL) and Web Application Description Language (WADL) describe functional service characteristics • Functional requirements: Requirements of the functionality which must be provided.

(Functions, Data, Behavior, etc.) • Non-functional requirements: Requirements of the circumstances under which the

functionality must be provided (e.g., reliability, performance, etc.) • WS are distributed over the Internet

• WS make use of existing ubiquitous transport Internet protocols like HTTP • By relying on the same well-understood transport mechanism as Web Content,

Web Services may leverage existing infrastructures and may cross corporate firewalls.

Introduction to Service Oriented Computing

11

Functional vs. Non-Functional Service Characteristics

• Functional Service Characteristics • Detail the operational characteristics that define the overall behavior of the

service • How the service is invoked • The location where it is invoked • Syntax of exchanged messages, etc.

• Typically a question of the system design ! • Non-Functional Service Characteristics

• Concentrate on service quality attributes • Service metering and cost • Performance metrics such as response time • Security attributes, authorization, authentication, transactional integrity,

scalability, etc. • Typically a question of the system architecture

Introduction to Service Oriented Computing

12

Tight versus loose coupling

Tight coupling Loose coupling

Physical coupling Direct physical link required Physical intermediary

Communication style Synchronous Asynchronous

Interaction pattern OO-style navigation of complex object trees Data-Centric, Self-Contained messages

Control of process logic Central control of process logic Distributed logic components

Underlying platforms Homogeneous Heterogeneous

Service discovery and binding Statically bound services Dynamically bound services

Platform dependencies Strong OS and programming language dependency OS- and programming language independent

• Coupling refers to the degree to which software components depend upon each other.

SOA

Introduction to Service-Oriented Computing

13

Web Services

▪ Types of Web services ! ▪ SOAP/WSDL based

▪ Service interface is exposed through WSDL documents ▪ Message exchange using SOAP ▪ Client code may be generated from WSDL description !

▪ Representational State Transfer (REST) ▪ Easy way to communicate with Web Services ▪ Resources are identified by URIs and their state is manipulated through HTTP

operations GET, POST, PUT, DELETE ▪ Rather a set of architectural principles, than a standard

Introduction to Service-Oriented Computing Characterizing Web Services - Integration scenarios